1. Field of the Invention
The present invention relates to an optical lens assembly for image taking, and more particularly to an optical lens assembly for image taking comprised of five lens elements to achieve the purpose of high resolution for applying to electronic products.
2. Description of the Related Art
In compact electronic products such as digital still cameras or mobile phone cameras, an optical lens assembly for image taking is generally installed for capturing images, and the optical lens assembly tends to be developed with a compact design and a low cost, while meeting the user requirements of good aberration correction, high resolution, and high image quality.
In general, a conventional optical lens assembly of a mini electronic product comes with different designs, including the two-lens, three-lens, four-lens, and five-or-more lens designs. However, if the image quality is taken into consideration, the optical lens assembly for image taking with the four-lens and five-lens designs have advantages on aberration correction and modulation transfer function (MTF) performance, wherein the five-lens design has a higher resolution than the four-lens design, thus being applicable for electronic products requiring high quality and high pixels.
In various compact optical lens assemblies for image taking with the five-lens design and a constant focal length, the prior art adopts different combinations of positive and negative refractive powers or a cemented doublet lens to shorten the total length of the optical system, or uses the fourth lens element and the fifth lens element with different refractive powers to build the optical system as disclosed in U.S. Pat. Publication Nos. 2004/0196571 and 2003/0117722, adopting a cemented single lens to shorten the total length of the optical system. However, the total length of the aforementioned conventional optical system is usually too long to suit compact electronic devices use.
In products such as compact digital cameras, webcams and mobile phone cameras, an optical lens assembly requires a compact design, a short focal length, and a good aberration correction. Among various designs of the optical lens assemblies for image taking with the five-lens design and a constant focal length, the fourth lens element or the fifth lens element having an inflection point is provided as disclosed in U.S. patents and publications including U.S. Pat. No. 7,826,151, 2010/0254029, and 2010/0253829, adopting the fourth lens element and the fifth lens element having an inflection point to tends towards the design with the shorter total length. In these prior arts, the fifth lens element with the inflection point is used for correcting the aberration or distortion of images, but the change of curvature of the fifth lens element is too large to be conducive to manufacture. In addition, these prior arts adopt the fourth lens element with stronger refractive power to shorten the total length of the optical lens assembly for image taking, such that the aberration produced by the fifth lens element cannot be corrected easily to meet the requirement. Therefore, the present invention provides a feasible design, adopts a combination of refractive powers, convex and concave surfaces of the five lens elements, and enables the fourth lens element and the fifth lens element to be with equal negative refractive powers, or applies the fourth lens element with weaker positive refractive power to achieve the effects of providing a high image quality and applying the optical lens assembly to compact electronic products that require high resolution.